Automatic motor control.



M. W. DAY. AUTOMATIC MOTOR CONTROL. APPLICATION FILED JULY 16, 1909.

1,028,332. Patented June 4, 1912.

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I I FTJYESSES/ mx @sm M. W. DAY. AUTOMATIC MOTOR CONTROL. APPLICATION FILED JULY 15, 1909.

Patented June 4, 1912.

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INYENTUH .A/IAXWELZ W DAY.

UNITED STATES Fii MAXWELL W. DAY, OF SCHENECTADY, NEVI YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

AUTOMATIC MOTOR CONTROL.

1,028,332, Specification of Letters Eatent. PatentedJune 4 11912, Application filed July 15, R209. Serial No. 507,843.

To all whom it may concern: for automatically establishing connections Be it known that I, MAXWELL W. DAY, a for retarding the motor, automatic means citizen of the United States, residing at operative upon a predetermined reduction Schenectady, county of Schenectady, State in the motor speed to control the retarding 5 f N Y k, h i t d rt in n w connections to prevent further retardation 60 and useful Improvements in Automatic of the motor speed.

Motor Control, of which the following is a In another aspect, my invention consists s ecific tion, in arranging the limit switch for automati- My invention relates to the automatic concally connecting the motor for dynamic trol of electric motors driving loads, such braking and providing automatic means re- 65 as hoists, elevators, etc.,vwhich have a defisponsive to a predetermined reduction in nite l1m1t to their traveh It has been custhe motor speed for changing the motor tomary to provide such motors with l1m1t connections from braking connections to low switches to open the motor circuit as the. speed drlving connections, so that the motor loadapproaches the limit of its travel and positively drives the load at reduced speed '70 sometimes to retard the motor before openuntil it is finally stopped.

ing its circuit. If the load varies, the point My invention will best be understood by at which it is brought to rest is not definitely reference "to the accompanying drawings, in

fixed by the limit switches ordinarily emwhich- 2Q ployed. With some kinds of loads the Figure 1 shows my invention applied to motor may run too far after its circuit is the controi of a motor driving a balance opened and with other loads not far enough, hoist or similar Wh le 2 shows or, if the load is brought up against a fixed applied to motor c stop or: spring buffer, under certain c ndihoist tions, the load may not reach the stop under other conditions it i ii "h bu -er too automatic I so here automa' ic mechanica in a other aspect, my my tarded and when operating at low speed.

H and H are resistances adapted to be connected in shunt to the motor armature for dynamic braking and also for weakening 5 the armature current for starting on light loads. J to J represent magnetically actuated switches or 'contactors controlling the motor circuit. The contactors J to J connect and disconnect the motor to and from the supply conductors. The .contactors J and J connect the motor for hoisting onev load and lowering the other and J and J for lowering the first load and hoisting the other. These two sets of contactors are interlocked through contacts j. Gontactors J and J control the resistances H and H contactors J 7 to J 9 control the resistances H, H and H and contactor J controls the magnetic friction brake E. K is a relay having its winding connected in shunt to the armature of'the motor so as to respond to variations in the armature voltage and, therefore, to variations in the motor speed.

With the switch F in off position the motor field is excited and a circuit is closed from the upper supply conductor C, through contact fingers f and f of switch F, through the winding of contactor J to 39 the lower supply conductor C. A circuit is also closed from the upper supply conductor 0, through contactj of contactor J 7 and the winding of contactor J 5 to the lower supply conductor 0. Contactors J 35 and J 6 are, therefore, energized, connecting resistance H v in shunt to the motor armature, the right-hand terminal of resistance H being connected permanently to the lower commutator brush while -the lefthand terminal is connected through the contact of contactor J to the upper brush. Thus, whenever the switch F is returned to ofi position, the motor is disconnected from the line and resistance H is connect- 5 ed in shunt to the armature to cause the motor. to act as a dynamic brake. For hoisting,'the switch F is moved first to the position indicated by the dotted line 1. A circuit is then closed from the upper conl duct-or C, through contact fingers jv and i through contactor coils J and J 8 in parallel, contact 7' of contactor J to the lower supply conductor. Another circuit is closed from the upper supply conductorCthrough contact fingers f and 1, contact fingers g and g of the limit switch and the winding of contactor J to the lowersupply conductor. The circuit last tra'ced closes the circuit of the brake winding E and releases 9 the friction brake, while the circuit first traced, by closing contactors J and J t, connects the motor armature to the line through resistances H, H and Hi. This circuit may be traced from the upper supply conductor, through contact of contactor J throiplgh the motorarmature to the left-hand terminal of resistance H through resistance H H and H, through contact of contactor J 8 to the lower supply conductor C. The resistance H remains in shunt to the motor armature in this first low speed position of the controller F1 In passing to the second position, indicate by dotted line 2, the circuit of contactor J 6 is broken at finger f so that resistances H and H in series are connected across the armature terminals, so that the current diverted from the armature is reduced; at the same time a circuit is closed throughcontact. finger f and contacts 9* and g on the limit switch through contactor windingJ". circuits resistance H so' as to increase the motor speed. In the third hoisting position of the switch F, acircuit is closed through contact finger f and contactor winding'J and contact 3'. Contactor J short-circuits resistance H further increasing the motor speed. In the fourth and last hoisting position the circuit is closed through contact finger f, contactor J and contact 9' of contactor J Contactor J short-circuits resistance H so that the mo- This contactor shorttor armature is now directly across the line. At the same time contact 7' opens the cirthe circuit of contact finger on the limit switch opens, which occurs when the contact fingers are in the position indicated by the third dotted line from the top. When this occurs, contactor coil J is open-circuited and opens its contacts inserting resistance H in series with the motor armature and by denergizing contactors Jand J 8 at contact j causes them to insert resistance H and H in series with the motor. Contactor J 5 is again energized through contact 7" and again connects resistances H and H in shunt to the motor armature, so that the motor is somewhat retarded. When the contact fingers of the limit switchreach the position indicated by the second dotted line from the top, contact finger g is engaged by its movable contact. .This closes the circuit from the upper su ply conductor C through contact. fingers f, f, g", g, contact of relay K and contactor 0011 J to the lower supply conductor 0. This. short-circuits resistance H so as to connect low resistance H in shunt to the motor armature and produces a strong dynamic braking action which efiectively retards the motor speed. This braking action continues until the speed and, conse uently, the armature voltage ofthe' motor ave fallen i so opens its contacts,-; deenerglzing. contactor ,J so as to open the braking connections and thereby leaving \the motor connected across the supply conductors with resistance H, H, and H in series with the motor armature andwith resistances H and H in shunt to the armature. The connections are thus changed from high speed connections to low speed driving connections and the load is, therefore, driven positively by the motor until it reaches the desired p0sition when it may be brought up against a fixed stop or stopped by the friction b rake. This last operation is performed. by the open-circuiting of contact 9 on the limit switch which opens the circuit of contactor coil J which deenergized the brake E and applies the friction brake. The current is still kept on the motor so that there is no possibility of the motor being driven backward by the load.' After the motor has been finally stopped the manually controlled switch F is returned to off position disconnecting the motor from the supply conductors.

The shunt connections of relay K may include, in addition to the motor armature, a port-ion of resistance H as shown, so as to impress on the relay a voltage somewhat higher than the armature voltage in order to enable it to hold up its contact until the armature voltage has fallen to a very low value, and to make less difference of voltage at the terminals of relay coil K between the voltage at which it picks up and full speed voltage.

With a balanced load, as shown in Fig. 1, the contacts of the limit switch G are symmetrical. If the load is unbalanced the limit switch may be arranged as in Fig. 2, in which two additional fingers 9 and g are applied to the limit switch between fingers g and 9 For hoisting the operation is precisely the same as has been described for Fig. 1, but in lowering the contact g is open-circuited at the same time that con tact finger g is open-circuited. The latter finger deenergizes the contactor J to apply the brakes as for hoisting while the finger deenergizes contactors J and J so as to disconnect the motor from the line. This modification is made, because, with an unbalanced load, the load when lowered tends to drive the motor forward so that there is no danger of the motor being driven backward between the time that the motor current is interrupted and the brake applied. f other reason for disconnecting the monn to ent it,-if the load brings from continuing to run so as to sla I do no to limit myself to the o ions and arrangement of parts shown described, but aim in the appended claims to cover all modifications which are within the scope of my invention. What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In combination, an electric motor, a load driven thereby, a limit switch for automat ically connecting said motor for dynamic braking, and automatic means rcsponsive to a predetermined reduction in motor speed for changing the motor connections from braking connections to low speed driving connections.

2. In combination, an electric motor, a load driven thereby, a limit switch for automatically connecting said motor for dynamic braking, and an electromagnetically controlled switch responsive to a predetermined drop in the motor armature voltage for changing the motor connections from braking connections to low speed driving connections.

3. In combination, an electric motor, a load driven thereby, a limit switch for automatically establishing connections for retarding the motor, and means operative upon a predetermined reduction in speed for cont-rolling the retarding connections and establishing driving connections.

4. In combination, an electric motor, a load driven thereby, a limit switch for short circuiting the motor armature through a resistance, and automatic means responsive to a predetermined reduction in motor speed for controlling the short circuiting connections and establishing driving connections.

5. In combination, an electric motor, a load driven thereby, a limit switch for automatically establishing connections for retarding the motor, and means responsive to a predetermined reduction in motor speed for controlling the retarding connections and establishing low speed driving connections.

6. In combination, an electric motor, a load driven thereby, automatically operating means for retarding the motor, and means whereby low speed driving connections for said motor are automatically established after the application of the retarding connections, and an automatically controlled mechanical brake for stopping said motor.

motor without breaking the driving con- 'nections.

10. In combination, an electric motor, a load driven thereby, a limit switch for automatically connecting said motor for dynamic brakin" an electromagnetically controlled switch responsive to a predetermined drop in the motor armature. voltage for changing the motor connections from braking connections to low speed driving connections, and automatically cont-rolled mechanical means for stopping said motor without breaking said low speed driving connections.

11. In combination, an electric motor, a

low speed drlvmg v load driven thereby, an electrically controlled mechanical brake, a limit swltch for inserting resistance in series with the, motor armature and connecting the motor for. dy-

namic braking, and means operative upon a predetermined reduction in motor speed for controlling the braking connections to permit the motor to continue running at reduced speed, said limit switch being arranged to control said mechanical brake to apply it after the motor speed has been reduced.

12. In combination, an electric motor, a load driven thereby, a manually controlled switch for controlling the supply of current 'tothe motor at starting, automatic means for dynamically braking the motor to retard the same to a predetermined sgeed and means for subsequently stopping t e motor without interrupting the supply of current thereto. 1 In witness whereof, I have hereunto set my hand this 14th day of July, 1909.

MAXWELL 'W. DAY.

Witnesses-z HELEN Onronn, 1 THOMAS W. NO0NAN.'. 

